Omni-directional radiation source and object locator

ABSTRACT

The current invention describes a method for determining azimuth and elevation angles of a radiation source or other physical objects located anywhere within an cylindrical field of view. The invention makes use of an omni-directional imaging system comprising of reflective surfaces, an image sensor and an optional optical filter for filtration of the desired wavelengths. The said imaging system is designed to view an omni-directional field of view using a single image sensor and with no need for mechanical scan for coverage of the full field of view. Use of two such systems separated by a known distance, each providing a different reading of azimuth and elevation angle of the same object, enables classic triangulation for determination of the actual location of the object. The invention is designed to enable use of low cost omni-directional imaging systems for location of radiation sources or objects. Many additional needs and applications are envisaged for such a method. Those needs include: location of flares and torches in search and rescue operations at sea or over land, detection of aircraft in close proximity for flight safety in VFR flight conditions, detection and location of weapon systems that employ Laser Range Finders, detection and warning of Laser Target Designators used in conjunction with surface launched or air dropped precision guided munitions, operation of Infra-red countermeasures, location of sparks resulted by enemy fire etc.

FIELD OF THE INVENTION

[0001] The invention relates to the field of omni-directional imaging.More specifically but not exclusively, it relates to the field oflocation of radiation sources and objects by using omni-directionalimaging systems.

DESCRIPTION OF RELATED ART

[0002] The present invention refers to a method for detection andlocation of radiation sources and physical objects in a cylindricalfield of view. Radiation source detection systems are widely used,mostly for military purposes. Current techniques are based on employmentof an imaging device with a focal plane array that is sensitive to aspecific wavelength, thus enabling detection of energy radiated in thisprecise wavelength. Detection of a radiation source is done by detectionof changes on the focal plane array—changes that occur only if a ray ofthe defined wavelength has penetrated the optical filter and came incontact with the focal plane array. Determination of the position(azimuth and elevation angles) of the radiation source is based onregistration of each pixel's elevation and azimuth. Employment of twosuch systems, each detecting the same radiation source and eachproducing a different azimuth and elevation angle enable determinationof the radiation source's exact location by classic triangulationmethods.

[0003] The mentioned method is currently used with imaging systems whichare able to cover only a relatively narrow field of view. Therefore, inorder to cover a field of regard that is wider than the field of viewcovered by the imaging system, it is customary to use several imagingsystems, each covers a different field of view. The use of severalimaging systems in such a solution necessitates accurate alignment ofthe systems to assure that each of them covers a different sector withno gaps or overlaps, and that all of them together cover the fullpanoramic view. It is also required that advanced synchronized softwarewill support all imaging devices and provide accurate readings andcalculation of the azimuth and elevation of the illuminating source. Dueto its complexity this method is considered cumbersome and costly.Another method commonly used is by rotating a conventional system aboutits axis to achieve coverage of a full panoramic field of regard.Rotation of such a system requires combination of smoothly movingmechanical component, accurately controlled and synchronized with thesoftware's operation to assure accurate determination of azimuth andelevation angles of the illuminating source.

[0004] The current invention provides a static staring imaging systemthat enables coverage of a full panoramic or nearly spherical field ofview, without mechanical movement or the need for multiple imagingsystems. The invention was disclosed in provisional patent No. 60/276933submitted by “Wave Group Ltd.”. The optical structures that enable theunique coverage of a full panoramic field of view or the nearlyspherical field of view are disclosed at provisional patent No.60/322737 submitted by “Wave Group Ltd.” and provisional patentapplication No. 60/22565 submitted by “Wave Group Ltd.”.

SUMMARY OF THE INVENTION

[0005] A first embodiment of the current invention provides a method fordetermining elevation angle of an object imaged by a focal plane arraysensor. Said focal plane array sensor is part of a focal plane arraythat images an omni-directional field of view. Said method comprises ofthe following stages:

[0006] a. Imaging a cylindrical field of view using an omni-directionalimaging system which comprises of an omni-directional lens assembly anda focal plane array.

[0007] b. Detection of an object imaged by a first sensor element on thesaid focal plane array.

[0008] c. Registration of the coordinates of said first sensor elementrelative to its position on the said focal plane array.

[0009] d. Registration of the coordinates of a second sensor elementwhich occupies the center of the entire image, relative to its positionon the said focal plane array.

[0010] e. Determination of the distance between said first sensorelement and said second sensor element.

[0011] f. Determination of a transformation function, which assigns eachsaid distance the appropriate elevation angle value, said transformationfunction is compatible to the design of the omni-directional imagingsystem.

[0012] g. Extraction of elevation angle value which corresponds to thesaid distance value from the said transformation function.

[0013] Preferably, said omni-directional lens assembly, which is a partof the omni-directional imaging system, comprises reflective lenses,which create a reflection of the omni-directional field of view towardsthe said focal plane array.

[0014] Said method, may further incorporate placement of an opticalfilter anywhere along the optical path of light rays that are capturedby the said omni-directional imaging system. Said optical filter isselected to insure filtration of specific wavelengths.

[0015] The said object that is detected by the said omni-directionalimaging system may be a radiation source. Said radiation source may emitin the visible or invisible spectrum.

[0016] Preferably, detection of said object or said radiation source onthe said focal plane array is accomplished by software processing of theimage that is captured by the said focal plane array.

[0017] Preferably, detection of said object on the said focal planearray is accomplished by employment of an electronic circuit, which isconnected to said focal plane array.

[0018] Preferably, said electronic circuit is designed to detect chargechanges on the said focal plane array and register the coordinates ofthe sensor elements on which changes have been detected.

[0019] A Second embodiment of the current invention provides a methodfor determining azimuth angle of an object imaged by a focal plane arraysensor. Said focal plane array sensor is part of a focal plane arraythat images an omni-directional field of view. Said method comprises ofthe following stages:

[0020] a. Imaging a cylindrical field of view using an omni-directionalimaging system which comprises of an omni-directional lens assembly anda focal plane array.

[0021] b. Detection of an object imaged by a first sensor element on thesaid focal plane array.

[0022] c. Registration of the coordinates of said first sensor elementrelative to its position on the said focal plane array.

[0023] d. Registration of the coordinates of a second sensor elementwhich occupies the center of the entire image, relative to its positionon the said focal plane array.

[0024] e. Determination of the distance between said first sensorelement and said second sensor element.

[0025] f. Superposition of a virtual two dimensional coordinate systemupon said focal plane array, in a way that the origin of said coordinatesystem coincides with the said second sensor element.

[0026] g. Alignment of one of the axes of said coordinate system withtrue north.

[0027] h. Determination of the angle between the line connecting saidfirst sensor element with said second sensor element and the axisaligned with true north—said angle being the azimuth angle

[0028] Preferably, said omni-directional lens assembly, which is a partof the omni-directional imaging system, comprises reflective lenses,which create a reflection of the omni-directional field of view towardsthe said focal plane array.

[0029] Said method, may further incorporate placement of an opticalfilter anywhere along the optical path of light rays that are capturedby the said omni-directional imaging system. Said optical filter isselected to insure filtration of specific wavelengths.

[0030] The said object that is detected by the said omni-directionalimaging system may be a radiation source. Said radiation source may emitin the visible or invisible spectrum.

[0031] Preferably, detection of said object or said radiation source onthe said focal plane array is accomplished by software processing of theimage that is captured by the said focal plane array.

[0032] Preferably, detection of said object on the said focal planearray is accomplished by employment of an electronic circuit, which isconnected to said focal plane array.

[0033] Preferably, said electronic circuit is designed to detect chargechanges on the said focal plane array and register the coordinates ofthe sensor elements on which changes have been detected.

[0034] The embodiments as described hereby enable determination ofazimuth and elevation angles of objects or radiation sources in thevisible or invisible spectrum, which are located in a cylindrical fieldof view, reflected towards a focal plane array by a lens assemblycomprises reflective lens or a plurality of lenses, and detected on thefocal plane array.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] For a better understanding of the invention and to show how thesame may be carried into effect, reference will now be made, purely byway of example, to the accompanying drawings. With specific referencenow to the drawings in detail, it is stressed that the particulars shownare by way of example and for purposes of illustrative discussion ofpreferred embodiments of the present invention only, and are presentedin the cause of providing what is believed to be the most useful andreadily understood description of the principles and conceptual aspectsof the invention. In this regard, no attempt is made to show structuraldetails of the invention in more detail than is necessary for afundamental understanding of the invention, the description taken withthe drawings making apparent to those skilled in the art how the severalforms of the invention may be embodied in practice. In the accompanyingdrawings:

[0036]FIG. 1 is a schematic description of an imaging device whichprovides a cylindrical field of view, and of the optical path of a lightbeam traveling within the imaging device.

[0037]FIG. 2 is a schematic description of an imaging device whichprovides a nearly spherical field of view and the optical path of alight beam traveling within the imaging device.

[0038]FIG. 3 is a brief schematic description of prior art, used todetermine azimuth and elevation angles of an object imaged by anarrow-angle imaging system.

[0039]FIG. 4 is a schematic description of the unique shape of the imageas acquired on the focal plane array of the imaging device.

[0040]FIG. 5 is a schematic description of a method for determination ofthe azimuth and elevation angles of the object or radiation source thatis imaged.

DETAILED DESCRIPTION

[0041] The preferred embodiments of the current invention providemethods for determining the azimuth and elevation angles of a radiationsource or object located in a cylindrical field of view and imaged by aFocal Plane Array (FPA) of an omni-directional imaging device. Thefollowing detailed description will refer, in brief, to the structure ofa few omni-directional imaging devices. It is stressed, that althoughonly several forms of structure are demonstrated, the method ofdetermining the azimuth and elevation angles of an object imaged bythese systems described hereby, is applicable to many other forms andstructures of omni-directional imaging devices that use reflectivesurfaces. Therefore the incorporation of figures and references tospecific models of omni-directional imaging devices is done purely byway of example, and should not be considered as limiting the extent ofthis invention.

[0042]FIG. 1 demonstrates detection of radiation (1), originating at aradiation source (2). The radiation (1) is reflected from anomni-directional mirror assembly (3) towards a focusing lens (4), anoptical filter (5) and a Focal Plane Array (6). Said omni-directionalmirror assembly (3) contains one or more reflective surfaces and isdesigned to enable a panoramic field of view. It is stressed thatalternative designs are possible for panoramic lens assemblies. Eachsuch design may enable a full panoramic view at different elevation anddepression angles, and specific designs can be determined according tothe desired applications and needs. It is further stressed that theoptical filter may be matched to wavelengths of radiation of interest.The optical filter may be employed anywhere along the optical path ofthe radiation as long as it is positioned before to the Focal PlaneArray. The radiation (1) is detected by one or more sensor elements (7)on the Focal Plane Array (6), for example by one or several pixels on aCharged Couple Device (CCD). The actual detection of a light beam may bedone by employment of an electronic circuit, connected to the FocalPlane Array and designed to detect charge changes or by means ofsoftware that examines or processes the output image.

[0043]FIG. 2 demonstrates detection of radiation (8) originating at afirst radiation source (9) and radiation (10) originating at a secondradiation source (11). The figure demonstrates an omni-directional lensassembly (12) which provides a nearly spherical field of view. By usingthis kind of lens assembly, it is possible to detect radiation sourcesor objects located within a cylindrical field of view around the imagingdevice, as well as radiation sources or objects located above theimaging device. The radiation (8) originating at the first radiationsource (9) is reflected inside the lens assembly (12) and towards afocusing lens (13), an optical filter (14) and a Focal Plane Array (15)and is detected by a sensor element or a group of sensor elements (16)on the Focal Plane Array (15). The radiation (10) originated at thesecond radiation source (11) penetrates the lens assembly (12) fromabove, passing through the lens assembly (12), the focusing lens (13),being filtered by the optical filter (14) and being detected by a sensorelement or a group of sensor elements (17) on the Focal Plane Array(15).

[0044]FIG. 3 is a schematic description of prior art, by whichdetermination of azimuth and elevation angles is made. This figurerefers to imaging systems which enable a conventional, narrow-anglefield of view. A scene (18) is imaged by a Focal Plane Array (19). It isstressed that the Focal Plane Array (19) is part of an entire imagingsystem, however, in order to simplify the explanation, reference is madeonly to the Focal Plane Array (1 9). The image produced by the FocalPlane Array (19) is that of a relatively narrow field of view. It isassumed that the size, in terms of angles, of the field of view coveredby the imaging device, is known and that the number of sensor elementsper line and per column on the Focal Plane Array is also known. Giventhis information, it is easy to determine how many sensor elements percolumn cover a single degree at elevation and how many sensor elementsper line cover a single degree in azimuth. Each sensor element on theFocal Plane Array (19) is assigned a coordinate which specifies its linenumber and column number. A point (20) in the scene is selected, inrespect to which, the center (21) of the Focal Plane Array is neitherelevated nor depressed or shifted in azimuth. An object (22) in thescene appears on a sensor element (23) on the Focal Plane Array.Elevation and azimuth angles of the object (22) need to be determined.Since the coordinates of the sensor element (23) that images the object(22) are known, and the coordinates sensor element which coincides withthe center (21) of the Focal Plane Array (19) are also known, it is easyto determine the distance of the sensor element (23) from the sensorelement that coincides with the center (21) on the Focal Plane Array(19). It is also known how many sensor elements per line and how manysensor elements per column cover a degree in space. All this informationis easily used to determine the azimuth and elevation angles of theobject (22). This well known method commonly used in prior art, is notapplicable when imaging a full panoramic field of view, since suchimaging devices incorporate reflective surfaces, which cause reflectionsand sometimes double reflections of the scene and distortions in waysother that in conventional imaging. The irregular reflection of thescene causes the image acquired by the focal plane array to have aunique shape, as illustrated below.

[0045]FIG. 4 is a schematic description of the shape of the imagecreated on a Focal Plane Array, when using an omni-directional imagingsystem, such as those demonstrated in FIGS. 1 and 2. In this figure, acircular image (24) is acquired by the Focal Plane Array (25). Thoseskilled in the art of omni-directional imaging would appreciate that thecircular image (24) actually consists of an outer circle (26) and aninner circle (27). When imaging a cylindrical field of view, the outercircle (26) will image the cylindrical field of view and the innercircle (27) will image a reflection of the lens that is inside theimaging system. When imaging a nearly spherical field of view, the outercircle (26) will image the cylindrical field of view from around theimaging device, whereas the inner circle (27) will image the field ofview above the imaging device.

[0046]FIG. 5 illustrates the manner in which determination of azimuthand elevation angles is made when using an omni-directional imagingsystem. This demonstration applies to objects located within thecylindrical field of view, imaged as the outer circle (26) on the focalplane array (25). In this figure, a sensor element (28) of the FocalPlane Array (25) images a radiation source or object located somewherewithin an omni-directional scene. For the purpose of illustration onlyit is assumed that the Focal Plane Array (25) is rectangular in shapeand that the circular image (24) is located exactly at center of theFocal Plane Array. The center (29) of the circular image (24) isdetermined and a virtual two dimensional coordinate system originatesfrom that center, having an “X” axis (30) and a “Y” axis (31), isimposed on it, its origin coinciding with the center of the circularimage (29). The virtual coordinate system is rotated so that the “X”axis (30) is aligned with true north. Each sensor on the Focal PlaneArray (25) is assigned a coordinate specifying its line number andcolumn number.

[0047] To determine the azimuth angle of an object or radiation sourcethat is imaged by a sensor (28) of the Focal Plane Array (25):

[0048] A virtual line (32) is formed, which connects the sensor elementcoinciding with the center of the circular image (29) with the sensorelement (28) which images the object of interest. Given the coordinatesof the two said sensors, and by using conventional trigonometry, theangle (33) between that line and any of the axes can be determined.

[0049] To determine the elevation angle of an object or radiation sourcethat is imaged by a sensor element (28) on the Focal Plane Array (25):

[0050] A virtual line (32) is formed, which connects the sensor elementcoinciding with the center of the circular image (29) with the sensorelement (28) which images the object of interest. Given the coordinatesof the two said sensors, it is easy to determine the length of thevirtual line (32) that connects them. The length of the virtual line(32) is used by a transformation function. The transformation functionassigns each “length” value, a corresponding elevation angle. Thetransformation function is determined according to the specific designand parameters of the omni-directional lens assembly and layout of theimaging system.

[0051] Those skilled in the art would appreciate that the transformationfunction is a product of the detailed optical design of the lensassembly. Since this invention does not refer to optical designparameters, and is not intended to serve as a guide in the process ofoptical design, no further reference is made to the transformationfunction. It is stressed however, that although the transformationfunction is needed for proper determination of elevation angles, thisfunction varies according to the specific design of the lens assembly,and is considered as given information to those skilled in the art ofoptical design.

[0052] It is further important to notice that the transformationfunction should produce different values according to the position ofthe imaging system itself. More explicitly, if the imaging system itselfit tilted (in elevation or in azimuth), the tilt angle is needed inorder to produce a true result regarding positions of objects thatappear in the image.

[0053] Referring to the current invention in general, it is stressedthat although reference was made to several kinds of omni-directionalimaging systems, including both cylindrical filed of view imagingdevices and nearly spherical field of view imaging devices, the azimuthand elevation measurement methods described hereby refer only to objectsappearing in the field of view acquired by the focal plane array afterreflection, which is the cylindrical field of view. It is important tonote that the nearly spherical field of view imaging device, producestwo different image sectors on the FPA. One image sector, referred to inFIG. 5 as the outer circle (26) comprises the cylindrical field of viewwhich is generated after reflection. The other image sector, referred toas the inner circle (27) comprises a landscape from above the imagingsystem, which is imposed as direct light through optical lenses and notas reflections from reflective surfaces. Therefore, when implementingthis method, it should be noticed, that the implementation is performedon image sectors that are acquired only after reflection, normally—by around mirror of axi-symmetrical shape.

What is claimed is:
 1. A method for determining elevation angle of anobject imaged by a focal plane array sensor, comprising the followingstages: a. Imaging a cylindrical field of view using an omni-directionalimaging system which comprises of an omni-directional lens assembly anda focal plane array. b. Detection of an object imaged by a first sensorelement on the said focal plane array. c. Registration of thecoordinates of said first sensor element relative to its position on thesaid focal plane array. d. Registration of the coordinates of a secondsensor element which occupies the center of the entire image, relativeto its position on the said focal plane array. e. Determination of thedistance between said first sensor element and said second sensorelement. f. Determination of a transformation function, which assignseach said distance the appropriate elevation angle value, saidtransformation function is compatible to the design of theomni-directional imaging system. g. Extraction of elevation angle valuewhich corresponds to the said distance value from the saidtransformation function. Wherein said focal plane array images anomni-directional field of view.
 2. A method of claim 1, wherein saidomni-directional lens assembly comprises reflective lenses.
 3. A methodof claim 1, wherein said detection of an object is accomplished bysoftware processing of the image.
 4. A method of claim 1, wherein saiddetection of an object is performed by an electronic circuit connectedto said focal plane array.
 5. An electronic circuit of claim 4, designedto detect charge changes on the said focal plane array and register thecoordinates of sensor elements in which changes have been detected.
 6. Amethod of claim 1, further comprising placement of an optical filter,anywhere along the optical path of light rays captured by the saidomni-directional imaging system, selected to insure filtration ofspecific wavelengths, and covering the entire field of view.
 7. Anoptical filter of claim 6, comprising of a multitude of optical filters.8. A method of claim 1, wherein said object is a radiation source.
 9. Aradiation source of claim 8, which emits in the visible spectrum.
 10. Aradiation source of claim 8, which emits in the invisible spectrum. 11.A method for determining azimuth angle of an object imaged by a focalplane array sensor, comprising the following stages: a. Imaging acylindrical field of view using an omni-directional imaging system whichcomprises of an omni-directional lens assembly and a focal plane array.b. Detection of an object imaged by a first sensor element on the saidfocal plane array. c. Registration of the coordinates of said firstsensor element relative to its position on the said focal plane array.d. Registration of the coordinates of a second sensor element whichoccupies the center of the entire image, relative to its position on thesaid focal plane array. e. Determination of the distance between saidfirst sensor element and said second sensor element. f. Superposition ofa virtual two dimensional coordinate system upon said focal plane array,in a way that the origin of said coordinate system coincides with thesaid second sensor element. g. Alignment of one of the axes of saidcoordinate system with true north. h. Determination of the angle betweenthe line connecting said first sensor element with said second sensorelement and the axis aligned with true north—said angle being theazimuth angle Wherein said focal plane array images an omni-directionalfield of view.
 12. A method of claim 11, wherein said omni-directionallens assembly comprises reflective lenses.
 13. A method of claim 11,wherein said detection of an object is accomplished by softwareprocessing of the image.
 14. A method of claim 11, wherein saiddetection of an object is performed by an electronic circuit connectedto said focal plane array.
 15. An electronic circuit of claim 14,designed to detect charge changes on the said focal plane array andregister the coordinates of sensor elements in which changes have beendetected.
 16. A method of claim 11, further comprising placement of anoptical filter, anywhere along the optical path of light rays capturedby the said omni-directional imaging system, selected to insurefiltration of specific wavelengths, and covering the entire field ofview.
 17. An optical filter of claim 16, comprising of a multitude ofoptical filters.
 18. A method of claim 11, wherein said object is aradiation source.
 19. A radiation source of claim 18, which emits in thevisible spectrum.
 20. A radiation source of claim 18, which emits in theinvisible spectrum.